The invention relates to magnetic recording heads and more specifically to a differential VGMR sensor.
The change in resistance caused by a magnetic field is called magnetoresistance. This phenomena has been exploited in recording head technology, for example, in computer mass storage devices such as tape and disk drives. Magnetoresistive recording heads are well known to be useful in reading back data from a magnetic media mass storage device such as a disk drive or magnetic tape drive. A magnetoresistive (xe2x80x9cMRxe2x80x9d) sensor detects magnetic field signals by measuring changes in the resistance of an MR element, fabricated of a magnetic material. Resistance of the MR element changes as a function of the strength and direction of magnetic flux being sensed by the element. Changes in resistance are then converted to determine the flux radiated from the magnetic medium. This measurement determines the signal stored on the medium.
Conventional MR sensors operate on the basis of the anisotropic magnetoresistive effect (xe2x80x9cAMRxe2x80x9d) in which a component of the element""s resistance varies as the square of the cosine of the angle between the magnetization vector of the MR element and the vector of a bias or sense current through the element:
xcfx81=xcfx81o+Dxcfx81cos2xcex8
where D92  is the component of resistance of interest and xcfx81o is the base resistance of the MR element.
A variety of multilayered structures demonstrate significantly greater sensitivity to magnetic fields from the recording medium. This effect is known as the giant magnetoresistive (xe2x80x9cGMRxe2x80x9d) effect. One type of sensor based on the GMR effect is called a vertical GMR (xe2x80x9cVGMRxe2x80x9d) sensor.
The GMR effect is due to spin dependent scattering of electrons from two or more magnetic layers, separated by nonmagnetic spacer layers.
As systems are pushed to higher read density, higher magnetic bit size or decreased recording media size, the available magnetic flux is decreased. In addition, sensitivity may be decreased from thermal noise. For example, while the head is flying over the disk surface, it may hit a particle (contamination). The energy of this collision will be dissipated in the form of heat causing the temperature of the head to increase, causing an increase in the resistance of the head ultimately resulting in a signal that may be even higher than the magnetic signal from a transition. In order to sense these smaller signals and increase areal density, read heads with greater sensitivities are needed.
Various implementations of the invention may include one or more of the following features.
In general, in one aspect, the invention feature an apparatus for reading data including a first magnetoresistive element, a second magnetoresistive element formed substantially parallel to the first magnetoresistive element, a nonmagnetic spacer interposed between the first and second magnetoresistive elements, wherein the first and second magnetoresistive elements are comprised of a first magnetic layer, a second magnetic layer formed substantially parallel to the first magnetic layer and a conductive spacer interposed between the first and second magnetic layers, wherein a bias current applied to the conductive spacer of the first magnetoresistive element is substantially equal and opposite to a bias current applied to the conductive spacer of the second magnetoresistive element.
In an implementation, the apparatus can further include a permanent magnet formed between the first and second magnetoresistive elements and adjacent the nonmagnetic spacer, a current strip formed between the first and second magnetoresistive elements and in between the nonmagnetic spacer and the permanent magnet, a current strip formed between the first and second magnetoresistive elements and adjacent the nonmagnetic spacer.
In an implementation, the first magnetic layer of at least one of the first and second magnetoresistive elements includes a first magnetic material, a second magnetic material, a spacing material interposed between the first and second magnetic materials.
In another implementation, the first and second magnetic materials are comprised of synthetic antiferromagnetics and the spacing material is ruthenium.
In another implementation, the second magnetic layer of at least one of the first and second magnetoresistive elements includes a first magnetic material, a second magnetic material, a spacing material interposed between the first and second magnetic materials.
In still another implementation, the first magnetic layer is a single layer, wherein the single layer can be comprised of at least one of NiFe, CoFe, and NiFeCo.
In yet another implementation, the apparatus of claim 1 wherein the first magnetic layer is a bilayer.
In another implementation, the apparatus further includes a first thin layer adjacent interposed between the first magnetic layer and the conductive spacer and a second thin layer interposed between the second magnetic layer and the conductive spacer, wherein the first and second thin layers can be comprised of at least one of Co and CoFe.
In another aspect, the invention features a VGMR sensor, including a first VGMR stack, a second VGMR stack and a nonmagnetic and nonconductive spacer interposed between the first and second VGMR stacks.
In an implementation, the first and second VGMR stacks includes a first SAF stack, a second SAF stack and a conductive spacer interposed between the first and second SAF stacks.
In another implementation, each of the first and second SAF stacks includes a first SAF layer, a second SAF layer and a spacer layer interposed between the first and second SAF layers, wherein the conductive spacer can be copper.
In another implementation, a current source to apply a first bias current to the first VGMR stack and a second bias current to the second VGMR stack are included.
In another implementation, the VGMR sensor can include a differential amplifier for summing the first and second bias currents and a detector for detecting changes in the first and second magnetizations.
In another aspect, the invention features a differential GMR sensor, including a plurality of spaced GMR stacks and means for biasing the magnetization of respective stacks to respond to external magnetic fields by increasing resistance in one stack and decreasing resistance in adjacent stacks.
The invention may provide one or more of the following advantages.
A differential VGMR sensor provided with two VGMR sensors which respond differently to an external field, thus producing a differential signal proportional to the field are provided. The sensor produces a better signal-to-noise ratio compared with a standard VGMR sensor. This better signal-to-noise ratio increases the read density of the sensor.